1. Technical Field
The present invention relates to integrated circuits in general, and in particular to a method for fabricating radiation-tolerant integrated circuit devices.
2. Description of Related Art
Most of today's high-density integrated circuit (IC) devices have been fabricated with complementary-metal-oxide semiconductor (CMOS) processing technology that is well-known to those skilled in the art of semiconductor processing. Two biggest advantages of CMOS IC devices are high noise immunity and low power dissipation. As such, CMOS IC devices are desirable in most commercial applications. However, standard CMOS IC devices may not be very suitable for aerospace applications because those environments tend to be characterized by high levels of radiation, particularly charged particles, and standard CMOS IC devices are notorious for having a relatively low radiation tolerance.
Prompt dose upset (PDU) and prompt dose transients (PDT) are terms used to describe a response of an electronic circuit to a radiation pulse. A radiation pulse generates multiple electron-hole pairs in the semiconductor material through an ionization process. The electrons are swept toward, and collected at the positive circuit nodes, creating a negative pulse. In conjunction, the holes are collected in the ground terminal(s). Because an electronic circuit has inherent impedance, the above-mentioned “photo-current” creates undesired voltage drops, resulting in a “rail-span collapse,” i.e., a collapse of voltage across the circuit nodes, which in turn cause logical or storage errors. The collapse of power rails in input/output (I/O) circuits create temporary transients, resulting in signal changes at the output of the I/O circuits. The effect of the radiation pulse worsens as power supply voltage is reduced with advance technologies (thus reducing the overhead margin), and with increase in device size and complexity (which increases the amount of photo-current).